This invention relates to a method and apparatus for forming metal roll-formed parts, and especially structural members such as are used in the manufacture of aircraft frames and is applicable to metal structural members made from raw material that is in the form of an elongate, generally flat or planar strip. The roll-formed parts are formed by a roll forming process into a non-planar configuration. An important application for this invention is the production of elongate structural members of the type known as hat sections and in particular hat sections having joggles or other portions having tapered or sloping surfaces. However, the invention and various aspects of the invention are useful for producing joggles or tapering or sloping surfaces portions in roll-formed parts having shapes other than hat sections.
As used in this application, a "joggle" is a shallow recess formed along a relatively short length of a complete structural member and usually along a planar or U-shaped portion thereof. Joggles of this type typically have a depth of about one metal thickness. For reasons discussed below, this type of joggle is referred to in industry as a "crush joggle." This is in contrast to a "full joggle" which is a generally S-shaped bend in a structural member created to displace the longitudinal center axis of the structural member from a first path located in a first plane to a second path located in a second plane which is parallel to the first plane.
The conventional method of forming a structural member with one or more joggles is to roll form the complete structural member. During the roll forming process, the flat metal strip is progressively bent about longitudinally- extending, imaginary lines, known as bend lines. Usually, the bend lines are straight for the entire length of the part and are located in horizontal planes which are either coincident with or parallel to the horizontal plane containing the longitudinal axis of the part being formed. After the structural member has been partly manufactured by use of a roll forming machine, and as a separate, non-continuous operation, any desired joggles in the part are formed in a press especially tooled to create the joggle by stamping or "crushing". (This is why this type of joggle is referred to as a "crush joggle".) To save on manufacturing time, several joggles in a structural member are crushed simultaneously with the use of a rather expensive piece of equipment. This process abruptly changes the shape of the structural member in the areas of the joggles and may cause excessive stresses in or strains on parts of the structural member as they are stretched or compressed in order to accommodate the formation of the joggles.
Other roll forming methods have been proposed to produce hat sections or other shapes with tapering heights or widths, including full joggles. Some may be capable of producing crush joggles. Examples of such methods are shown in the following patent documents:
Brooks et al U.S. Pat. No. 3,756,057 PA0 Colbath U.S. Pat. No. 3,903,723 PA0 Foster U.S. Pat. No. 4,006,167 PA0 Trishevsky et al U.S. Pat. No. 4,588,577
Matsukura Japanese patent application 61-86031
As the above documents reveal, the known methods either have limited capabilities or require the use of highly complex, sophisticated and expensive machinery.